Screen arrangement for stirring mills

ABSTRACT

A closed stirring mill for processing solid materials in liquids having a stirrer and a plurality of spherical grinding elements and a screen arrangement at the ground material outlet to hold back the grinding elements wherein the screen arrangement consists of one or more screen cartridges attached to the jacket wall or the cover plate of the mill.

United States Patent 91 Wilhelm 1 SCREEN ARRANGEMENT FOR STIRRING MILLS [75] Inventor: Karl-Heinz Wilhelm, Bobstadt,

Germany [73] Assignee: Firma Draiswerke GmbH,

Manheim, Germany 22 Filed: July 19, 1971 211 App]. No.: 163,672

[30] Foreign Application Priority Data July 28, 1970 Germany P 20 37 258.1

[52] US. Cl. 241/172, 241/69 [51] Int. Cl. B02c 13/284, B02c 17/16 [58] Field of Search 241/69, 70, 172,

[56] References Cited UNITED STATES PATENTS 3,050,263 Barkman et a1. 241/172 X Dec. 25, 1973 3,337,140 8/1967 Wahl 241/172 X 2,562,560 7/1951 Macartney... 241/69 X 2,670,139 2/1954 Treshow 241/70 3,339,896 9/1967 McKibben 241/172 X 3,486,705 12/1969 Szeguari 241/172 3,545,687 12/1970 Mosby 241/69 X Primary Examiner-Harold D. Whitehead Assistant Examiner-E. F. Desmond Attorney-Alvin Browdy and Sheridan Neimark [5 7] ABSTRACT A closed stirring mill for processing solid materials in liquids having a stirrer and a plurality of spherical grinding elements and a screen arrangement at the ground material outlet to hold back the grinding elements wherein the screen arrangement consists of one or more screen cartridges attached to the jacket wall or the cover plate of the mill.

10 Claims, 4 Drawing Figures PATENTEUuEcesmn 3.780.957 SHEET 20F 3 I N VE NTOR.

PATENIE-Dnzczs ms 3; 780.957 SHEET 30F 3 FIGA INVENTORPT,

SCREEN ARRANGEMENT FOR STIRRING MILLS The invention concerns a closed stirring mill, intendedfor crushingand distribution of solids in liquids. The mill housing generally mounted in an upright position, is provided with a high-speed stirrer, with the material to be ground suspended in a liquid passing continuously through the mill housing, from bottom to top in a standing stirring mill. This process takes place in the presence of spherical grinding elements, which serve to crushand pulverize the material to be ground. A flow which disperses the materials to be ground within the mill is produced by thestirrer together with the numerous grinding elements. Frequently, spherical grinding elements which have only a very small diameter (e.g., a diameter in the range from 0.2 to 3 mm) are used in such stirring mills.

The grinding elements in the dispersed material to be ground must be separated from this material at the outlet of the stirring mill. This process poses considerable difficulties, especially when the grinding elements in the stirring mill are of small diameter.

The use of (for example) cylindrical screens at the upper end of the jacket wall of the mill housing are known to be used as a screening system at the outlet of the stirring mill. This screen arrangement does not disturb the arrangement of the drive for the stirring shaft with the stirring disks. However, when a flat screen is installed at the upper outlet of the stirring mill, the drive for the stirrer must be fed through this flat screen.

In the case of horizontal stirring mills, it is known that a double-walled disk screen element can be mounted at the outlet of the stirring mill, i.e., at the end of the mill housing at which the stirring mill is not driven through the screen element.

In evaluating this known screen arrangement for stirring mills, we must proceed on the basis that the screen arrangement is subjected to a relatively high degree of wear under the prevailing operating conditions. For this reason, and also because of the cleaning operations that must be performed from time to time, it is especially valuable to have exchangeability or replacement for the screen which is used in the installation. In the case of the cylindrical screen, as well as the flat screen and the double-walled disk screen element, simple removal or exhange of such a screen is not possible without first (for example) removing the cover plate of the stirring mill. Modern technology generally uses closed stirring mills today, in which the removal of the known screen systems also poses difficulties.

The invention is designed particularly to overcome these difficulties. A screen arrangement is proposed which insures convenient exchange and replacement, while providing a sufficiently large screen area. Moreover, the invention places particular emphasis on the fact that the screen surface can be exposed on all sides to the flow of the dispersed material being ground.

Consequently, the invention consists primarily of the fact that the screen arrangement consists of one or more tubular screen cartridges, which extend into the internal space of the mill housing and have their open ends (directed outward) connected to the material outlet. Thus, the arrangement can be designed advantageously so that one or more screen cartridges can be installed at the outlet of the mill housing, in suitable openings in the jacket wall of the mill housing. According to a further advantageous embodiment of the invention, a screen cartridge can be mounted laterally on each side of the drive shaft for the stirrer. It is also advantageous to provide a screen cartridge perpendicular with the drive shaft of the stirrer, which has its free end mounted closely adjacent to the drive shaft of the stirrer. In this way, it is possible to insure that the use of a screen arrangement in the form of screen cartridges will in no way disturb the drive for the stirrer shaft or the form of the stirrer shaft with its stirring elements. It is also intended that this system of screen cartridges will in no way impede the flow of the material being ground from having its full effect in the entire mill housing up to the cover plate of the stirring mill. This also means (and particular emphasis is placed on it according to the invention) that the screen cartridge is exposed over its entire surface to the flow of material being ground. It is also provided that the use of the screen cartridges makes it particularly easy to expose a sufficiently large screen area to the flow of material being ground, without the internal space of the mill housing being particularly affected in terms of its size by the screen arrangement. It means that the internal space of the mill housing can be used for the actual grinding and pulverizing process in the resultant disperse flow of material being ground all the way to the cover plate.

The arrangement according to the invention means that no dead spaces remain within the mill housing, which are not affected by the flow of material being ground to some extent. The accumulation of residue in such dead spaces" has a particularly unfavorable effect on the quality of the product. Avoiding these dead spaces also means that any residue that may remain can be washed away when the machine is cleaned with a detergent, because the detergent is able to capture all residues from the disperse material being ground as it flows into the entire internal space.

These advantages of the object of the application are still more effective if the screen cartridge or cartridges according to the invention are mounted axially parallel to the drive shaft of the stirrer in openings in the cover plate of the stirring mill. This can insure that the screen cartridges are connected with a collecting area related to the material outlet for the stirring mill, in order to insure the emptying of the dispersed ground material from the stirring mill.

The screen cartridges can be fastened in the cover plate by means of a rim flange using a screw cap, with the cavity in this screw cap being connected by a radial channel to a cylindrical collecting chamber mounted around the shaft bearing and hence connected with the outlet channel.

With this type of arrangement for the object of the invention, the entire screen surface of the screen cartridges is exposed in a particularly favorable manner to the flow of material being ground. The screw caps may be conveniently removed from the cover plate. The removal of the screen cartridges and the possible replacement of one screen cartridge by a new screen cartridge is quick and convenient to accomplish, without having to remove the cover plate itself from the closed stirring mill.

Usually the drive as well as the main bearing for the type of stirring mill in question is mounted above the cover plate. In such a design, an elastic rubber ring may be interposed between the cover plate and the mill housing of the stirring mill. This means that the cover plate does not have a rigid and unchanging position within the mill housing with the stirring mechanism as well as the screen cartridges. often the stirring mechanism (and the screen cartridges as well) can oscillate to some extent. This elastic mounting of the stirring mechanism and the screen cartridges on the mill housing removes the load on the shaft seal and insures that no dead spaces remain in the mill housing, in which residue from the material being ground could remain and not be removed by a flow of detergent.

The drawing shows examples of the object of the invention as follows:

FIG. 1: A stirring mill in schematic representation.

FIG. 2: The upper end of a stirring mill, with screen assembly in lengthwise cross section.

FIG. 3: A section through the stirring mill along line Ill-III in FIG. 2, and

FIG. 4: A further design of the screen arrangement at the upper end of the stirring mill.

An electric drive motor 102 is mounted in the vertical position by its flange 103 to an arm 100 on a machine stand 101. The mill housing 1 of a stirring mill is mounted vertically below the drive motor 102, with a stirring shaft 2 driven at high speed by drive motor 102 extending into said stirring mill. The stirring shaft is overhung in the bearing housing 104 in the vicinity of the motor, and is therefore no longer supported at its other end, located in mill housing 1. Stirring shaft 2 carries a number of stirring disks 3, fastened to the stirring shaft by screws 3a. The vertical stirring mill is closed at its upper end. In order to avoid radial movements of the stirring shaft 3 against shaft seals 7a in a gasket housing 7, the stirring shaft 3 is mounted in said gasket housing 7 by means of ball bearings 7b (FIG. 4). The gasket housing 7 is itself elastically mounted, by means of elastic annular disk 4, which is bolted to mill housing 1 with the aid of rings 5 and 6 on one side by means of another ring 5a, and on the other side to the gasket housing 7 for stirring shaft 2. The elastic annular disk 4 insures thst stirring shaft 2, which is mounted only at its upper end in bearing housing 104, can execute lateral oscillating movements together with its stirring disks 3 to a certain slight extent. The gasket housing 7 is prevented from turning by means of one or more locking pins 6a, firmly mounted in a ring 6 and loosely mounted in another ring 5. As is generally the case, the material to be ground is fed into the mill housing 1 at the lower end through an inlet stub 105. The internal space of the mill housing is filled 50 to 70 percent with small, spherical grinding elements, which can have (for example) a diameter of 0.2 to 3 mm. A disperse flow of material being ground develops in the mill housing due to the introduction of the material to be ground, said flow moving from bottom to top. The ground material leaves the stirring mill through an outlet stub 8, which is screwed on to a corresponding flange 8b of mill housing 1, a seal 80 being provided between them. In the example of the embodiment of the invention shown in FIGS. 2 and 3, three tubular screen cartridges, 9, l0 and 11 are connected to this outlet stub. These screen cartridges are introduced laterally at the upper end of mill housing 1 through the jacket wall of mill housing 1. These screen cartridges are located in housings 12, 13, 14, which are placed in corresponding openings in the jacket wall of mill housing 1 and have their flanges a against the upper edges of housings l2, 13, 14 in this case with a ring seal 10b mounted between. They are held in this position by the connecting flange 8b of outlet stub 8. Screen cartridges 9, l0, 11 can be removed and replaced again simply by unscrewing outlet stub 8, without having to remove the cover plate of the stirring mill.

Screen cartridges 9 and 11 are installed laterally with respect to the stirring shaft 2, while screen cartridge 10 is shorter and is mounted close to stirring shaft 2.

The screen cartridges are made of a fine-mesh braid or punched thin sheet. They have bottoms made of the same material or of sheet.

The arrangement of these screen cartridges therefore has no effect on the drive of the stirrer by means of stirring shaft 2. It is also possible to have another stirring disk 3 mounted above screen cartridges 9, 10 and 11 on stirring shaft 2. But even without this upper stirring disk, not shown in the drawing, the use of the screen arrangement with the aid of these screen cartridges insures that the disperse flow of ground material has a complete effect from the bottom of the stirring mill all the way to the cover plate of this stirring mill, i.e., the screen cartridges are exposed on all sides to the flow of ground material.

According to the embodiment of the invention shown in FIG. 4, two screen cartridges 15 and 16 with top edge flanges 17 and 18, each of which is mounted firmly against a corresponding shoulder 17a, 18a in cover plate 21, are mounted firmly in cover plate 21 by means of screw caps 19 and 20. Each of the screw caps 19 and 20 is screwed into cover plate 21 by means of a four-cornered shaft 22, 23. Screw caps 19 and 20 are each provided with a cavity 24, 25. These cavities 24 and 25 are connected by radial channels 26, 27, 29 in screw caps 19 and 20 to a collecting chamber 30 in cover plate 21 which has a cylindrical shape and surrounds gasket housing 7, said collecting chamber emptying into an outlet stub 32.

In this case also, the disperse flow of ground material moves upward from the bottom of the stirring mill. The flow washes over screen cartridges l5 and 16. With the grinding elements being held back against the outer wall of the screen cartridges, the finished ground material passes through the fine-mesh screen surfaces into spaces 24, 25 in screw caps 19, 20. From there the ground material flows through radial channels 26, 27, 29 and collecting chamber 30 to outlet stub 32.

It is obvious that the replacement of screen cartridges 15 and 16, either for purposes of cleaning or for installing a new screen cartridge, can be accomplished very conveniently by unscrewing the corresponding screw caps 19 and 20. There is no need to remove cover plate 21 from mill housing 1 on the stirring mill.

In order for the stirring shaft 2 together with cover plate 21 and screen cartridges 15 and 16 to execute a slight oscillating movement in this case as well, cover plate 21 is connected to mill housing 1 by a flexible rubber ring 33.

It will be obvious to those skilled in the art that various changes may be made without departing from the spirit of the invention and therefore the invention is not limited to what is shown in the drawings and described in the specification, but only as indicated in the appended claims.

What is claimed is:

1. In a closed stirring mill for processing solid materials in liquids with a vertical mill housing having ajacket wall and a cover plate with an aperture therein, and a stirrer driven by a drive shaft, said drive shaft extending through said aperture, and said mill housing having material inlet and outlet openings thereon and spherical grinding elements therein, wherein a disperse flow of ground material is produced in the presence of said spherical grinding elements by high-speed stirring and in which a screen arrangement is provided at said material outlet to hold back the said grinding elements, the improvement wherein said screen arrangement comprises at least one cartridge having a cylindrical screen and having an open end, said cartridge extending into the internal space of said mill housing and being connected at the open end thereof to said material outlet wherein substantially the entire surface of the cartridge is exposed to the flow of the material being ground.

2. A stirring mill according to claim 1, wherein the said screen cartridges are installed at said ground material outlet of said mill housing through suitable openings in said jacket wall of said mill housing.

3. A stirring mill according to claim 2, wherein one screen cartridge is mounted laterally on each side of said drive shaft of said stirrer.

4. A stirring mill according to claim 3, wherein one screen cartridge is mounted perpendicularly to said drive shaft of said stirrer.

5. A stirring mill according to claim 1, wherein said screen cartridges are mounted parallel to said drive shaft of said stirrer in openings in said cover plate of said stirring mill.

6. A stirring mill according to claim 5 further including a collecting chamber linked to said material outlet to carry off the disperse ground material from the stirring mill, wherein said screen cartridges are connected to said collecting chamber.

7. A stirring mill according to claim 6, wherein said screen cartridges further include edge flanges at the open end thereof, and further including screw caps for fastening said edge flanges to said cover plate, wherein said screw caps have hollow spaces therein connected by way of radial channels to said collecting chamber.

8. In a stirring mill according to claim 1 further including a drive means attached to said drive shaft and located above said cover plate for driving said drive shaft, the improvement further comprising a flexible rubber ring between said cover plate and said jacket wall.

9. A stirring mill according to claim 1 wherein said outlet opening is located near the top of said housing.

10. A stirring mill in accordance with claim 1 wherein the cylindrical wall of said cartridges is made of a fine-mesh metal braid or perforated thin sheet and wherein the end opposite the open end thereof is made of the same material or of sheet. 

1. In a closed stirring mill for processing solid materials in liquids with a vertical mill housing having a jacket wall and a cover plate with an aperture therein, and a stirrer driven by a drive shaft, said drive shaft extending through said aperture, and said mill housing having material inlet and outlet openings thereon and spherical grinding elements therein, wherein a disperse flow of ground material is produced in the presence of said spherical grinding elements by high-speed stirring and in which a screen arrangement is provided at said material outlet to hold back the said grinding elements, the improvement wherein said screen arrangement comprises at least one cartridge having a cylindrical screen and having an open end, said cartridge extending into the internal space of said mill housing and being connected at the open end thereof to said material outlet wherein substantially the entire surface of the cartridge is exposeD to the flow of the material being ground.
 2. A stirring mill according to claim 1, wherein the said screen cartridges are installed at said ground material outlet of said mill housing through suitable openings in said jacket wall of said mill housing.
 3. A stirring mill according to claim 2, wherein one screen cartridge is mounted laterally on each side of said drive shaft of said stirrer.
 4. A stirring mill according to claim 3, wherein one screen cartridge is mounted perpendicularly to said drive shaft of said stirrer.
 5. A stirring mill according to claim 1, wherein said screen cartridges are mounted parallel to said drive shaft of said stirrer in openings in said cover plate of said stirring mill.
 6. A stirring mill according to claim 5 further including a collecting chamber linked to said material outlet to carry off the disperse ground material from the stirring mill, wherein said screen cartridges are connected to said collecting chamber.
 7. A stirring mill according to claim 6, wherein said screen cartridges further include edge flanges at the open end thereof, and further including screw caps for fastening said edge flanges to said cover plate, wherein said screw caps have hollow spaces therein connected by way of radial channels to said collecting chamber.
 8. In a stirring mill according to claim 1 further including a drive means attached to said drive shaft and located above said cover plate for driving said drive shaft, the improvement further comprising a flexible rubber ring between said cover plate and said jacket wall.
 9. A stirring mill according to claim 1 wherein said outlet opening is located near the top of said housing.
 10. A stirring mill in accordance with claim 1 wherein the cylindrical wall of said cartridges is made of a fine-mesh metal braid or perforated thin sheet and wherein the end opposite the open end thereof is made of the same material or of sheet. 